SUM and COUNT/ja
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世界各国のプロフィール: 集計関数
このチュートリアルでは COUNT, SUM , AVG などの集計関数を扱う。集計関数は多数の値から１つの値を計算する。例えば、関数 SUM は 2, 4 ,5 から1つの値 11 を計算する。
| name | continent | area | population | gdp |
|---|---|---|---|---|
| Afghanistan | Asia | 652230 | 25500100 | 20343000000 |
| Albania | Europe | 28748 | 2831741 | 12960000000 |
| Algeria | Africa | 2381741 | 37100000 | 188681000000 |
| Andorra | Europe | 468 | 78115 | 3712000000 |
| Angola | Africa | 1246700 | 20609294 | 100990000000 |
| ... | ||||
以下の例を見ておくとよい。
SUM, Count, MAX, DISTINCT と ORDER BY の利用
世界人口のトータル
世界の総人口を表示。（各国の人口を合計）
world(name, continent, area, population, gdp)
SELECT SUM(population)
FROM world
SELECT SUM(population)
FROM world
大陸のリスト
大陸名を重複しないように表示。
SELECT DISTINCT(continent)
FROM world
アフリカのGDP
アフリカAfrica の各国のgdpの合計を求める。
SELECT SUM(gdp)
FROM world
WHERE continent = 'Africa'
大きな国の数
面積が少なくとも 1000000 以上の国の数を求める。
SELECT COUNT(name)
FROM world
WHERE area >= 1000000
バルト三国の人口
'Estonia', 'Latvia', 'Lithuania' の人口合計を求める。
SELECT SUM(population)
FROM world
WHERE name IN ('Estonia', 'Latvia', 'Lithuania')
GROUP BY と HAVING の使用方法
この例を見てもよい: Using GROUP BY and HAVING./ja
各大陸の国の数を数える
各大陸continentごとに大陸名continentとそこの国の数を表示する。
SELECT continent, COUNT(name)
FROM world
GROUP BY(continent)
各大陸の大きな国を数える
各大陸の人口が10000000人以上の国を数え、大陸名とその数を表示する。
SELECT continent, COUNT(name)
FROM world
WHERE population >= 10000000
GROUP BY(continent)
大きな大陸を数える
その大陸の各国の人口の合計が100000000人以上の大陸のリストを表示する
SELECT continent
FROM world
GROUP BY continent
HAVING SUM(population)>= 100000000
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